Peripheral nerve stimulator

ABSTRACT

An electronic peripheral nerve stimulator is disclosed, the nerve stimulator comprising a power supply, a transistorized oscillator circuit coupled to the power supply and including at least one transistor and a resistance-capacitance network defining the oscillation frequency of the oscillator. The transistor is coupled in circuit with the resistance-capacitance network and means are provided to vary the effective impedance of the resistance-capacitance network to provide a selective output pulse repetition rate from the oscillator circuit. A transformer is provided, the transformer having a first primary winding coupled in circuit with the collector of the transistor, a secondary primary winding coupled in circuit with the base of the transistor and through which a &#39;&#39;&#39;&#39;reflected&#39;&#39;&#39;&#39; current is passed by way of a positive feedback loop to the transistor base, and a secondary winding from which an output pulse is obtained.

United States Patent [72] 3,295,528 1/1967 Masaki 128/422 Longueville, New South Wales, Australia 3,311,11 1 3/1967 Bowers 128/422 [21] P Primary Examiner-William E. Kamm [22] F'led l Attorney-Holman & Stern [45] Patented Oct. 12, 1971 [73] Assignee The Wellcome Foundation Limited London, England I [32] Pnomy 3 ABSTRACT: An electronic peripheral nerve stimulator is dis- [33] Austraha closed, the nerve stimulator comprising a power supply, a [31] 32o43/68 transistorized oscillator circuit coupled to the power supply and including at least one transistor and a resistance- [54] PERIPHERAL NERVE STIMULATOR capacitance network defining the oscillation frequency of the 6Claims, 1 Drawing Fig oscillator. The trans1stor is coupled in circuit with the resistance-capacitance network and means are provided to vary U-S. the efie tive im edan e of the resistance capacitance net. 1 331/112 work to provide a selective output pulse repetition rate from [51] Int. Cl A6lu l/36 the oscillator circuit A t f r is provided, the trans- [50] Fleld of Search 128/421, former having a first primary winding coupled in circuit with 422; 331/1 12 the collector of the transistor, a secondary primary winding coupled in circuit with the base of the transistor and throu h [56] Rdemnces Cited which a reflected current is passed by way of a posin /e UNITED STATES PATENTS feedback loop to the transistor base, and a secondary winding 3,050,695 8/ 1962 DuVall l28/42l X from which an output pulse is obtained.

Inventor John E. Colyer 1 PERIPHERAL NERVE STIMULATOR This invention relates to an improved, preferably portable,

.electronic peripheral nerve stimulator'for applying stimuli to a patient.

The stimulator in accordance withthe present invention (as hereinafter defined) is adapted, interalia, to monitor the effects of a muscle relaxant drug on theneuromuscular junction of a muscle or muscle group in a patient, or to enable the effect of such a drug .to be detected and reversed or counteracted, or to determine whether the cause of muscular relaxation is due to the presence of muscle relaxants or to an effect on or by the central nervous system.

During surgery it is often necessary to know the type, duration of action and intensity of neuromuscular blockade present in a patient; i.e., for example, whether the blockadeis produced by a depolorizing or nondepolorizing relaxant drug. These specific aspects of the action of the relaxants can be determined by nerve stimulation.

n the other hand it may, in the course of surgery, be necessary that the voluntary muscles in the area where a surgeon is working be relaxed or paralyzed so that they cannot contract or move as the surgeon works. This is achieved by administering a neuromuscular blocking agent (muscle relaxant drug) and, thereafter, continued monitoring of a neuromuscular junction enables incremental doses of relaxant to be administered in time to prevent unwanted movement of the muscles occuring.

Similarly, it may be required to counteract the effect of the muscle relaxant drug to facilitate study of a patients condition during a postoperative period.

Furthermore it may be desirable to identify, during the course of surgery, nerves or nervous tissues by stimulation and thereby obtaining a response from associated muscle groups.

The present invention has for its objects 'toprovide an-electrical nerve stimulator for the purposes above mentioned and which is capable of providing either or intermittent output pulses over a wide (variable) frequency range, which has a low power source drain (this being an important consideration for surgery use where it is imperative that it should not fail during prolonged operating periods), which preferably has a variable voltage output, and which is safe for use in operating theatres where highly inflammable gases may be encountered.

Thus, a peripheral nerve stimulator in accordance with the present invention comprises a power supply, a transistorized oscillator circuit including at least one transistor in circuit with a resistance-capacitance network, the effective impedance value of which is variable to achieve a desired output pulse repetition rate, anda transformer having a first primary winding in circuit with the collector of said transistor, a second primary winding in circuit with the base of said transistor and through which a "reflected" current is passed by way of a positive feedback loop to said transistor base, and a tertiary winding from which an output pulse may be obtained.

Preferably, a gas dischargelamp is connected in series with said tertiary winding, and means are preferably connected in circuit with said gas-discharge lamp and said tertiary winding for adjusting the voltage of said output pulses to a desired level.

The invention will be better understood from the following description of a preferred embodiment thereof taken in conjunction with the accompanying drawing; this comprising a circuit diagram of the device.

From the drawing, the peripheral nerve stimulator generally comprises a power supply, an oscillator circuit employing a single transistor VTl in conjunction with a pulse transformer (or ringing choke) T1 and the pulse repetition rate of which is controlled by a R-C network, and an output circuit connected to the secondary winding of said transformer.

The fundamental operation of the circuit is based upon a modified "blocking oscillator." Capacitor Cl initially has zero voltage across it but charges to a negative potential through the timing resistor network R -R (or through a single timing resistor as the case may be) until such time as the voltage across Cl exceeds the base-emitter forward conduction voltage of the transistor WI. The transistor base then conducts and collector current is drawn through a first primary winding W1 of the transformer T1. The current through winding W1 is reflected into a second primary winding W2 and, through positive feedback, turns the transistor "on" hard. This gives a short rise time to the base, and therefore collector, current pulse.

The additional base bias supplied from the reflected pulse permits the base current to discharge capacitor C1 to a very low level. Base current is desirably limited to a safe value by introduction of a series limiting resistor R6.

After the pulse from the collector circuit has decayed transistor VTl is cutoff, since the voltage across Cl again approaches zero, and the circuit can no longerring. One pulse only is thus generated.

The cycle then repeats as capacitor C1 charges through resistor network R -R,, a train of single pulses being generated by the circuit for as long as the power supply is switched-on, in this case by switch S1 ganged to a potentiometer RVl hereinafter referred to.

The pulse repetition rate is dependent upon the time constant of the R.C. network, this, as shown in the drawing,being made variable by the resistor switching arrangementcomprising switch S2 and pushbuttons S3 and S4, but, in a much simplified embodiment, being fixed by a single timing resistor. The valve of capacity of Cl must be selected such that transistor W1 is initially fully tumed on," the resistor(s) being the main timing element(s).

The collector current pulse in winding W1 is also reflected into the secondary winding W3 and across which a high voltage pulse is developed, the value of which is determined by the primary to secondary winding ratio.

This high-voltage pulse feeds into a series connection of a gas-discharge (neon) lamp LP! and potentiometer RVl. The

gas-discharge lamp LPl serves both as a visual indicator of the presence of an output pulse and to limit the voltage present across the potentiometer RVl.

Output connections SKl and 5K2 are taken from the moving arm and one side of the potentiometer RVl respectively, the voltage across the load being regulatory by adjustment of the potentiometer arm.

To facilitate improved operation of the circuit above described, a resistor R5 is connected in parallel with capacitor C1, a resistor R5 is connected in parallel with capacitor C1, a resistor R7 is connected in parallel with the gas-discharge lamp LPI, a resistor R8 is connected in parallel with the potentiometer and a resistor R9 is connected in series with the moving arm of the potentiometer.

From a practical viewpoint, resistor R5 has the effect of stabilizing the firingpoint of transistor VT] and helps to compensate for variations in the capacitance of capacitor C1. Resistor R7 stabilizes the firing point of the lamp LPl and prevents the occurrence of large peak voltages across winding W3 during the instant before gas ionization in the lamp LPI. The resistor R8 is employed purely to act as an output voltage adjustment, the value being chosen such that the no-load output voltage is of a desired value and thus compensates for variations in component parameters. The value of resistor R9 is chosen so as to provide optimum compensation for variations in load resistance, so as to achieve an approximately linear law for output voltage against potentiometer rotation for all values of load resistance within a-working range.

Many modifications may be made in the circuit as described above and as illustrated without departing from the scope of the invention. However, the following are given by way of exemplification as components and component values which may be employed to construct such a device, the elements referred to being those shown in the drawing:

Battery, 6 volt (4Xl.5

volt size AA pencil cue) Resistor R], 470K ohms Resistor R2, 270K ohms Resistor R3, 56K ohms Resistor R4, lOOOK ohms Resistor R5, IOOK ohms Resistor R6, 22 ohms Resistor R7, 330K ohms Resistor R8, 33K ohms Resistor R9, i000 ohms Potentiometer RV l 25 K ohms, linear Capacitor Cl, 200 micro Farads (6 Volt working) Transistor, Germanium PNP type 2N2l7 Transformer, "Ferguson" type TSWl 12 All of time-resistors above-mentioned are 0.5 watt carbon type and although optimum values are specified for resistors R8 and R9, these should be selected for a desired peak noload voltage and for optimum control linearity respectively.

With the various discussed components having values as above indicated, the following results have been found obtainable:

a. Output voltage-O to 375 volts (no load, open circuit condition) to 220 volts 1,000 ohms load resistance) b. Pulse rise time -less than 1.0 microsecond c. Pulse width-approx. 1.3 milliseconds (overall) d. Pulse repetition rate -l pulse/ 10 secs. (slide switch S2 to left) 1 pulse/ secs. (slide switch S2 to right) --l pulse/sec. pushbutton S3 operated).

50 pulses/sec. (pushbutton S4 operated).

From the foregoing it will be appreciated that the two position switch S2 permits the selection of continuous automatically cycling twitch stimulus" frequencies of one pulse per 5 or second intervals. Operation of pushbutton S3 effects the automatic selection of a continuous twitch-stimulus frequency of one pulse per second but this will revert to the 5 to 10 second pulse rate immediately the pushbutton is released. Similarly, a maximum tetanic stimulus" rate of 50 pulses per second will be obtained for as long as the pushbutton S4 is depressed.

A container for the components aforedescribed may be formed of any suitable plastic material, the cover therefor being apertured to permit the mounting of external projection of the lamp LPl, switch S2, pushbuttons S3 and S4 and a control knob for the ganged potentiometer/switch S1. The cover may additionally be marked with suitable indicia and the con tainer apertured to take a connectable probe or electrode lead plug.

Electrodes for use in conjunction with the device in accordance with the present invention may take the form of plate electrodes, needle electrodes or, for convenience, probes.

lclaim:

1. An electronic peripheral nerve stimulator comprising, a power supply, a transistorized oscillator circuit coupled to said power supply and including at least one transistor and resistance-capacitance network defining the oscillation frequency of said oscillator, said resistance-capactiance network and the emitter-collector path of said transistor each being coupled in parallel circuit across said power supply, means to vary the effective impedance of said resistance-capacitance network to provide a selective output pulse repetition rate from said oscillator circuit within the range of one pulse per l0 seconds to 50 pulses per second, and a transformer, said transformer having a first primary winding, means coupling said first primary winding in circuit between the collector of the transistor and said power supply, a second primary winding, means coupling said second primary winding in circuit between the base of the transistor 3 a point on said resistancecapacitance network, said last-mentioned means defining a positive feedback loop through which a reflected" current is passed to said transistor base, and secondary winding from which an output pulse is obtained.

2. An electronic peripheral nerve stimulator as claimed in claim 1, wherein said resistance-capacitance network comprises a single capacitor and four series connected resistors and defines the pulse repetition rate said means to vary the effective impedance including means connecting three of said resistors to be selectively switched out of circuit, whereby a variable pulse repetition rate is provided.

3. An electronic peripheral nerve stimulator as claimed in claim 2, wherein the values of said resistors are selected to provide respective pulse repetition rates of one pulse per 10 seconds, one pulse per 5 seconds, one pulse per second, and 50 pulses per second, respectively.

4. An electronic peripheral nerve stimulator as claimed in claim 1, together with a gas discharge lamp connected in series with said secondary winding.

5. An electronic peripheral nerve stimulator as claimed in claim 2, together with a potential divider means connnected in circuit with said tertiary winding for adjusting the voltage level of said output pulses.

6. An electronic peripheral nerve stimulator as claimed in claim 3 together with potential divider means connected in circuit with said secondary winding for adjusting the voltage level of said output pulses.

Disclaimer 3,612,060.J0lm E. Oolyer, Longueville, New South Wa1es,'Australia. PE-

RIPHERAL NERVE STIMULATOR. Patent dated Oct. 12, 1971. gisclaimer filed Apr. 20, 1978, by the assignee, Burroughs Wellcome 0. Hereby enters this disclaimer to all claims in said patent.

[Ofiioial Gazette June 13, 1.978.] 

1. An electronic peripheral nerve stimulator comprising, a power supply, a transistorized oscillator circuit coupled to said power supply and including at least one transistor and resistancecapacitance network defining the oscillation frequency of said oscillator, said resistance-capactiance network and the emittercollector path of said transistor each being coupled in parallel circuit across said power supply, means to vary the effective impedance of said resistance-capacitance network to provide a selective output pulse repetition rate from said oscillator circuit within the range of one pulse per 10 seconds to 50 pulses per second, and a transformer, said transformer having a first primary winding, means coupling said first primary winding in circuit between the collector of the transistor and said power supply, a second primary winding, means coupling said second primary winding in circuit between the base of the transistor a a point on said resistance-capacitance network, said last-mentioned means defining a positive feedback loop through which a ''''reflected'''' current is passed to said transistor base, and secondary winding from which an output pulse is obtained.
 2. An electronic peripheral nerve stimulator as claimed in claim 1, wherein said resistance-capacitance network comprises a single capacitor and four series connected resistors and defines the pulse repetition rate said means to vary the effective impedance including means connecting three of said resistors to be selectively switched out of circuit, whereby a variable pulse repetition rate is provided.
 3. An electronic peripheral nerve stimulator as claimed in claim 2, wherein the values of said resistors are selected to provide respective pulse repetition rates of one pulse per 10 seconds, one pulse per 5 seconds, one pulse per second, and 50 pulses per second, respectively.
 4. An electronic peripheral nerve stimulator as claimed in claim 1, together with a gas discharge lamp connected in series with said secondary winding.
 5. An electronic peripheral nerve stimulator as claimed in claim 2, together with a potential divider means connnected in circuit with said tertiary winding for adjusting the voltage level of said output pulses.
 6. An electronic peripheral nerve stimulator as claimed in claim 3 together with potential divider means connected in circuit with said secondary winding for adjusting the voltage level of said output pulses. 